From 87fe9db4675e510ea9c0234429b4773341c4e86d Mon Sep 17 00:00:00 2001
From: Patrick Cloke <clokep@users.noreply.github.com>
Date: Tue, 27 Sep 2022 10:47:34 -0400
Subject: [PATCH] Support the stable dir parameter for /relations. (#13920)

Since MSC3715 has passed FCP, the stable parameter can be used.

This currently falls back to the unstable parameter if the stable
parameter is not provided (and MSC3715 support is enabled in
the configuration).
---
 changelog.d/13920.feature           |  1 +
 synapse/rest/client/relations.py    | 24 +++++++++++++++---------
 tests/rest/client/test_relations.py |  6 ++----
 3 files changed, 18 insertions(+), 13 deletions(-)
 create mode 100644 changelog.d/13920.feature

diff --git a/changelog.d/13920.feature b/changelog.d/13920.feature
new file mode 100644
index 000000000000..aee702bcd269
--- /dev/null
+++ b/changelog.d/13920.feature
@@ -0,0 +1 @@
+Support a `dir` parameter on the `/relations` endpoint per [MSC3715](https://github.com/matrix-org/matrix-doc/pull/3715).
diff --git a/synapse/rest/client/relations.py b/synapse/rest/client/relations.py
index ce970800136a..205c556f64b6 100644
--- a/synapse/rest/client/relations.py
+++ b/synapse/rest/client/relations.py
@@ -56,15 +56,21 @@ async def on_GET(
         requester = await self.auth.get_user_by_req(request, allow_guest=True)
 
         limit = parse_integer(request, "limit", default=5)
-        if self._msc3715_enabled:
-            direction = parse_string(
-                request,
-                "org.matrix.msc3715.dir",
-                default="b",
-                allowed_values=["f", "b"],
-            )
-        else:
-            direction = "b"
+        # Fetch the direction parameter, if provided.
+        #
+        # TODO Use PaginationConfig.from_request when the unstable parameter is
+        #      no longer needed.
+        direction = parse_string(request, "dir", allowed_values=["f", "b"])
+        if direction is None:
+            if self._msc3715_enabled:
+                direction = parse_string(
+                    request,
+                    "org.matrix.msc3715.dir",
+                    default="b",
+                    allowed_values=["f", "b"],
+                )
+            else:
+                direction = "b"
         from_token_str = parse_string(request, "from")
         to_token_str = parse_string(request, "to")
 
diff --git a/tests/rest/client/test_relations.py b/tests/rest/client/test_relations.py
index d33e34d82957..fef3b72d76b0 100644
--- a/tests/rest/client/test_relations.py
+++ b/tests/rest/client/test_relations.py
@@ -728,7 +728,6 @@ def test_background_update(self) -> None:
 
 
 class RelationPaginationTestCase(BaseRelationsTestCase):
-    @unittest.override_config({"experimental_features": {"msc3715_enabled": True}})
     def test_basic_paginate_relations(self) -> None:
         """Tests that calling pagination API correctly the latest relations."""
         channel = self._send_relation(RelationTypes.ANNOTATION, "m.reaction", "a")
@@ -771,7 +770,7 @@ def test_basic_paginate_relations(self) -> None:
         channel = self.make_request(
             "GET",
             f"/_matrix/client/v1/rooms/{self.room}/relations"
-            f"/{self.parent_id}?limit=1&org.matrix.msc3715.dir=f",
+            f"/{self.parent_id}?limit=1&dir=f",
             access_token=self.user_token,
         )
         self.assertEqual(200, channel.code, channel.json_body)
@@ -788,7 +787,6 @@ def test_basic_paginate_relations(self) -> None:
             channel.json_body["chunk"][0],
         )
 
-    @unittest.override_config({"experimental_features": {"msc3715_enabled": True}})
     def test_repeated_paginate_relations(self) -> None:
         """Test that if we paginate using a limit and tokens then we get the
         expected events.
@@ -838,7 +836,7 @@ def test_repeated_paginate_relations(self) -> None:
 
             channel = self.make_request(
                 "GET",
-                f"/_matrix/client/v1/rooms/{self.room}/relations/{self.parent_id}?org.matrix.msc3715.dir=f&limit=3{from_token}",
+                f"/_matrix/client/v1/rooms/{self.room}/relations/{self.parent_id}?dir=f&limit=3{from_token}",
                 access_token=self.user_token,
             )
             self.assertEqual(200, channel.code, channel.json_body)